Daily habits · Free · Private
Water intake calculator — how much should I drink a day?
Estimate how much fluid you need each day based on sex, exercise, hot weather, pregnancy and breastfeeding, with practical tips on staying hydrated.
Where the numbers come from
The baseline uses adequate intakes from the US National Academies of Sciences, Engineering, and Medicine: about 3.7 litres of total water a day for men, 2.7 litres for women, 3.0 litres in pregnancy and 3.8 litres while breastfeeding. We assume about 80% comes from drinks, then add roughly 0.35 litres for every 30 minutes of exercise and 0.5 litres for hot conditions.
Simple hydration habits
- Drink with every meal and keep a refillable bottle nearby.
- Check your urine: pale yellow usually means you are drinking enough.
- Drink before, during and after exercise, and more in heat.
- Older adults may feel less thirsty, so planned drinks help.
Some people need less. If you have heart failure, kidney disease or liver disease, or take medicines that affect fluid balance, follow your clinician's fluid advice. Drinking very large amounts quickly can be dangerous.
Signs of dehydration
Thirst, dark urine, dry mouth, tiredness, headache and dizziness are common. Seek care for confusion, fainting, a very fast heartbeat, no urine for 8 hours or more, or dehydration in a baby or older person.
Frequently asked questions
Do I really need eight glasses of water a day?
Needs vary. The US National Academies set adequate total water intakes of about 3.7 litres a day for men and 2.7 litres for women, from all drinks and food. About 80% usually comes from drinks.
Do tea and coffee count?
Yes. Water, milk, tea and coffee all count toward fluid intake. Water is the best everyday choice because it has no sugar or calories.
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